1. Field of the Invention
This invention relates to a lubricating oil for compressors of refrigerators using therein a hydrogen-containing halogenocarbon as a refrigerant (the oil being hereinafter referred to as xe2x80x9ca refrigerator oil for use with a hydrogen-containing halogenocarbon refrigerantxe2x80x9d) and, more specifically, it relates to such a refrigerator oil which comprises a specific ester as a base oil and is superior in various properties.
2. Prior Art
Generally, naphthenic mineral oils, paraffinic mineral oils, alkylbenzenes, polyglycolic oils, ester oils and mixtures thereof, which have each a kinematic viscosity of 10-200 cSt at 40xc2x0 C., as well as these oils incorporated with suitable additives have been used as refrigerator oils.
On the other hand, chlorofluorocarbons (CFCS) type refrigerants, such as CFC-11, CFC-12, CFC-113 and HCFC-22, have been used for refrigerators.
Of these CFCS, CFCS such as CFC-11, CFC-12 and CFC-113, which are obtained by substituting all the hydrogen atoms of hydrocarbons thereof by halogen atoms including chlorine atoms, may lead to the destruction of the ozone layer, and therefore, the use of the CFCS has been controlled. Accordingly, hydrogen-containing halogenocarbons, such as HFC-134a and HFC-152a, have been being used as substitutes for CFCs. HFC-134a is especially promising as a substitute refrigerant since it is similar in thermodynamic properties to CFC-12 which has heretofore been used in many kinds of refrigerators of home cold-storage chests, air-conditioners and the like.
Refrigerator oils require various properties, among which their compatibility with refrigerants is extremely important in regard to lubricity and system efficiency in refrigerators. However, conventional refrigerator oils comprising, as the base oils, naphthenic oils, paraffinic oils, alkylbenzenes, heretofore known ester oils and the like, are hardly compatible with hydrogen-containing halogenocarbons such as HFC-134a. Therefore, if said conventional refrigerator oils are used in combination with HFC-134a, the resulting mixture will separate into two layers at normal temperature so as to degrade the oil-returnability which is the most important within the refrigeration system and cause various troubles such as a decrease in refrigeration efficiency, the deterioration of lubricity and the consequent seizure of the compressor within the system whereby the refrigerator oils are made unsuitable for use as such. In addition, polyglycolic oils are also known as refrigerator oils for their high viscosity index and are disclosed in, for example, JP-A-57-42119 and JP-A-61-52880 and JP-A-57-51795. However, the polyglycolic oils disclosed in these prior art publications are not fully compatible with HFC-134a thereby raising the same problems as above and rendering them unusable.
Further, U.S. Pat. No. 4,755,316 discloses polyglycolic refrigerator oils which are compatible with HFC-134a and U.S. Pat. No. 4,851,144 discloses refrigerator oils comprising a mixture of an ester and a polyglycol which are compatible with HFC-134a. In addition, the present inventors developed polyglycolic refrigerator oils which have excellent compatibility with HFC-134a as compared with conventional known refrigerator oils, filed an application for a patent for the thus developed polyglycolic refrigerator oils and have already obtained a patent (U.S. Pat. No. 4,948,525) therefor. It has been found, however, that the polyglycolic oils raise problems as to their high compatibility with water and inferior electrical insulating property.
On the other hand, refrigerator oils used in compressors of home refrigerators and the like are required to have a high electrical insulating property. Among the known refrigerator oils, alkylbenzenes and the mineral oils have the highest insulating property, but they are hardly compatible with hydrogen-containing halogenocarbons such as HFC-134a as mentioned above. WO 90/12849 describes a composition comprising a hydrogen-containing halogenocarbon and a specific ester lubricant. Therefore, no refrigerator oil having both high compatibility with hydrogen-containing halogenocarbons such as HFC-134a and a high insulating property has been developed prior to the present invention.
The present inventors made various intensive studies in attempts to develop refrigerator oils which can meet the aforesaid requirements and, as the result of their studies, they found that esters having specific structures have excellent compatibility with hydrogen-containing halogenocarbons such as HFC-134a, and a high electrical insulating property as well as excellent lubricity. This invention is based on this finding.
The object of this invention is to provide refrigerator oils for use with hydrogen-containing halogenocarbons refrigerants, the oils comprising as a major component (or a base oil) at least one kind of ester having a specific structure and an epoxy compound and having excellent compatibility with hydrogen-containing halogenocarbons such as HFC-134a, high electrical insulating property, high wear resistance, low hygroscopicity, and high thermal and chemical stability.
The present invention provides a refrigerator oil for use in compressors using therein a hydrogen-containing halogenocarbon as a refrigerant, consisting essentially of as a base oil at least one ester selected from the group consisting of:
[I] a pentaerythritol ester represented by the general formula (1) 
wherein R1-R4 may be identical with or different from each other and are each selected from the group consisting of straight-chain alkyl groups having 3 to 11 carbon atoms, branched-chain alkyl groups having 3 to 15 carbon atoms and cycloalkyl groups having 6 to 12 carbon atoms, the straight-chain alkyl groups being present in a ratio of not more than 60% of the total alkyl groups, and a is an integer of 1 to 3;
[II] a polyol ester represented by the general formula (2) 
wherein R5-R7 may be identical with or different from each other and are each selected from the group consisting of straight-chain alkyl groups having 3 to 11 carbon atoms, branched-chain alkyl groups having 3 to 15 carbon atoms and cycloalkyl groups having 6 to 12 carbon atoms, the straight-chain alkyl groups being present in a ratio of not more than 60% of the total alkyl groups, R8 is selected from the group consisting of methyl, ethyl and propyl groups, and b is an integer of 1 to 3;
[III] an ester represented by the general formula (3) 
wherein X1 is a group represented by the general formula xe2x80x94OR11 or 
X2 is a group represented by the general formula 
R9 and R15 are each a divalent hydrocarbon group having 1 to 8 carbon atoms, R10 and R12 are each a divalent saturated hydrocarbon group having 2 to 16 carbon atoms, R11 and R16 are each a branched-chain alkyl group having 3 to 15 carbon atoms, R13 and R14 are each a branched-chain alkyl group having 3 to 14 carbon atoms, c and e are each an integer of 0 or 1 and d is an integer of 0 to 30; and
[IV] a polyol ester obtained by the synthesis of, as raw materials, (a) a neopentyl type polyhydric alcohol having 5 to 6 carbon atoms and 3 to 4 hydroxyl groups, (b) a straight-chain monocarboxylic acid and/or a branched-chain monocarboxylic acid, the branched-chain monocarboxylic acid being present in a ratio of not less than 50 mol % of the total monocarboxylic acids, (c) a dicarboxylic acid: and further comprising at least one epoxy compound.
First, the pentaerythritol esters [I] will be explained in detail. In the formula (1), R1-R4 may be identical with, or different from, each other and are each a group selected from the group consisting of straight-chain alkyl groups having 3-11 carbon atoms, preferably 3-7 carbon atoms, branched-chain alkyl groups having 3-15 carbon atoms, preferably 4-11 carbon atoms and cycloalkyl groups having 6-12 carbon atoms, preferably 6-8 carbon atoms. The cycloalkyl groups in this invention may include alkylcycloalkyl groups. In addition, the ratio of the straight-chain alkyl groups to the total alkyl groups is not more than 60%, preferably not more than 50%. Further, a is an integer of 1-3. Thus, the formula(1) illustrates monopentaerythritol esters, dipentaerythritol esters and tripentaerythritol esters.
R1-R4 are each exemplified by n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, iso-propyl group, iso-butyl group, iso-pentyl group, iso-hexyl group, iso-heptyl group, iso-octyl group, iso-nonyl group, iso-decyl group, iso-undecyl group, iso-dodecyl group, iso-tridecyl group, iso-tetradecyl group, iso-pentadecyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, cycloundecyl group, cyclododecyl group, methylcyclohexyl group, ethylcyclohexyl group, propylcyclohexyl group, butylcyclohexyl group, pentylcyclohexyl group or hexylcyclohexyl group.
The pentaerythritol esters [I] are esters of pentaerythritol, dipentaerythritol or tripentaerythritol and a monocarboxylic acid, and are ordinarily obtained by the reaction of pentaerythritol,dipentaerythritol, tripentaerythritol or a mixture thereof with a mixture of at least one carboxylic acid having the aforementioned alkyl group.
Secondly, the polyol esters [II] will be explained in detail. In the formula (2), R5-R7 may be identical with, or different from, each other and are each a group selected from the group consisting of straight-chain alkyl groups having 3-11 carbon atoms, preferably 3-7 carbon atoms, branched-chain alkyl groups having 3-15 carbon atoms, preferably 4-11 carbon atoms and cycloalkyl groups having 6-12 carbon atoms, preferably 6-8 carbon atoms. The cycloalkyl groups in this invention may include alkylcycloalkyl groups. With respect to the above R5-R7, the ratio of the straight-chain alkyl groups to the total alkyl groups (including cycloalkyl groups) is not more than 60%, preferably not more than 50%. In addition, R8 is a group selected from the group consisting of methyl group, ethyl group and propyl group. Further, b is an integer of 1-3. Thus, the formula (2) illustrates trimethylolethane esters, trimethylolpropane esters, trimethylolbutane esters and dimers-trimers thereof.
R5-R7 are each exemplified by n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, iso-propyl group, iso-butyl group, iso-pentyl group, iso-hexyl group, iso-heptyl group, iso-octyl group, iso-nonyl group, iso-decyl group, iso-undecyl group, iso-dodecyl group, iso-tridecyl group, iso-tetradecyl group, iso-pentadecyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, cycloundecyl group, cyclododecyl group, methylcyclohexyl group, ethylcyclohexyl group, propylcyclohexyl group, butylcyclohexyl group, pentylcyclohexyl group or hexylcyclohexyl group.
The polyol esters [II] are esters of trimethylolethane, trimethylolpropane, trimethylolbutane or a dimer or trimer thereof and a monocarboxylic acid, and are ordinarily obtained by the reaction of trimethylolethane, trimethylolpropane, trimethylolbutane, a dimer or trimer thereof or a mixture thereof with a mixture of at least one carboxylic acid having the aforementioned alkyl group.
Thirdly, the esters [III] will be explained in detail. In the formula (3), X1 is a group represented by the general formula xe2x80x94OR11 or 
and X2 is a group represented by the general formula 
In addition, R9 and R15 are each a divalent hydrocarbon group having 1-8 carbon atoms, preferably 1-6 carbon atoms, R10 and R12 are each a divalent saturated hydrocarbon group having 2-16 carbon atoms, preferably 2-9 carbon atoms, R11 and R16 are each an alkyl group having 1-15 carbon atoms, preferably 1-12 carbon atoms, and R13 and R14 are each an alkyl group having 1-14 carbon atoms, preferably 1-11 carbon atoms. Further, c and e are each an integer of 0 or 1 and d is an integer of 0-30, preferably 1-30.
R9 and R15 are each exemplified by a methylene group, ethylene group, propylene group, trimethylene group, butylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, phenylene group, other unsaturated hydrocarbon groups or the like. R10 and R12 are each illustrated by nonamethylene group, decamethylene group, undecamethylene group, dodecamethylene group, tridecamethylene group, tetradecamethylene group, pentadecamethylene group, hexadecamethylene group, cyclohexylene group or the like in addition to the above alkylene groups (except for methylene group). R13 and R14 are each concretely exemplified by straight- or branched-chain alkyl groups, such as methyl group. ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group or tetradecyl group. R11 and R16 are each illustrated by a straight- or branched-chain alkyl group, such as a pentadecyl group, in addition to any one of the above alkyl groups.
The method for producing the esters [III] is not particularly limited. For example, a mixture of the esters [III] can be produced by the esterification reaction of (i) a diol having none of ether linkages in the branched-chains thereof with (ii) a dicarboxylic acid and (iii) a monocarboxylic acid and/or (iv) a monohydric alcohol. The esters [III] are also produced by the reaction of the diol (i) with the monocarboxylic acid (iii) or the reaction of the dicarboxylic acid (ii) with the monohydric alcohol (iii).
The diols (i) used herein are those having 2-16 carbon atoms and are exemplified by alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, heptamethylene glycol, octamethylene glycol, nonamethylene glycol, decamethylene glycol, neopentyl glycol, 2-ethyl-2-methyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,4-pentanediol, 2-methyl-2,4-pentanediol, 2-methyl-1,6-hexane, 1,4-cyclohexane dimethanol and 2,2-bis(4-hydroxycyclohexyl)propane.
The dicarboxylic acids (ii) used herein are those having 2-10 carbon atoms and are exemplified by saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, methylmalonic acid, ethylmalonic acid, dimethylmalonic acid, methylsuccinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethylsuccinic acid, 2-ethyl-2-methylsuccinic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3,3-dimethylglutaric acid and 3-methyladipic acid; unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid and mesaconic acid; and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid.
The monocarboxylic acids (iii) used herein are those having 2-15 carbon atoms and are exemplified by acetic acid, propionic acid. butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, 3-methylbutanoic acid, 2-methylbutanoic acid, 2-ethylhexanoic acid, 2,4-dimethylpentanoic acid, 3,3,5-trimethylhexanoic acid and benzoic acid.
The monohydric alcohols (iv) used herein are those having 1-15 carbon atoms and are exemplified by methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, unedecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, isopropanol, isobutanol, 2-methyl-1-butanol, 2,2-dimethyl-1-propanol, 3,3-dimethyl-1-butanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 2,4,4-trimethyl-1-pentanol, 2,2,4-trimethyl-1-pentanol, 2-ethyl-4-methyl-1-pentanol and 2-ethyl-1-hexanol.
The molecular weight of the ester [III] is not particularly limited, but the number average molecular weight of the ester [III] is In the range of preferably 200-3000, more preferably 300-2000, to improve the compressor in sealability.
Fourthly, the polyol ester [IV] will be explained in detail.
The neopentyl type polyhydric alcohols (a) having 5-6 carbon atoms and 3-4 hydroxyl groups are illustrated by trimethylolethane, trimethylolpropane and pentaerythritol.
The monocarboxylic acids (b) preferably used herein are those having 2-15 carbon atoms and are exemplified by acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid and pentadecanoic acid.
These carboxylic acids may be either straight-chain or branched-chain ones, but it is preferable to use the latter having a branched-chain structure in an amount of not less than 50 mol %, preferably not less than 60 mol %.
The dicarboxylic acids (c) used herein are those having 2-10 carbon atoms and are exemplified by saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, methylmalonic acid, ethylmalonic acid, dimethylmalonic acid, methylsuccinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethylsuccinic acid, 2-ethyl-2-methylsuccinic acid, 2-methylglutaric acid, 3-methylglutaric acid and 3-methyladipic acid; unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid and mesaconic acid; and aromatic dicarboxylic acids such as phthalic acid, terephthalic acid and isophthalic acid.
The esters [IV] are produced by the esterification reaction of the aforesaid component (a) with the component (b) and the component (c) under ordinary esterification conditions, for example, in the presence of an acid catalyst such as sulfuric acid and at an temperature of 100-180xc2x0 C.
The chemical structure of the ester [IV] according to the present invention is illustrated by the following general formula (6) 
wherein X3 and X4 may be identical with, or different from, each other and are each an alkyl group having 1-4 carbon atoms or a group represented by the general formula 
R26-R29 and R31 may be identical with, or different from each other and are each an alkyl group having 4-15 carbon atoms; R30 is an alkylene group having 1-8 carbon atoms; j is an integer of 0 or 1; and k is an integer of 1-5.
The molecular weight of the polyol ester [IV] is not particularly limited, but the number average molecular weight of the ester [IV] is in the range of preferably 200-3000, more preferably 300-2000, to improve the compressor in sealability.
The products obtained by the methods as mentioned above may be refined to remove the by-products and/or unreacted reactants, but the by-products and/or unreacted reactants may be present in small amounts in the refrigerator oils of the present invention as far as they do not impair the excellent performances thereof.
In the preparation of the refrigerator oils of the present invention, the esters [I]-[IV] mentioned above may be used singly, or jointly as a mixture of at least two kinds of the esters.
The kinematic viscosities of the esters according to the present invention are in the range of preferably 2-150 cSt, more preferably 5-100 cSt at 100xc2x0 C.
The refrigerator oil of the present invention may comprise as the only base oil at least one member selected from the above esters [I]-[IV] and, as required, it may additionally comprise other base oils for refrigerator oils. Among the other base oils, preferable ones are illustrated as follows:
a polyoxyalkylene glycol or an ether thereof represented by the general formula (4) 
wherein R17 and R18 are each a hydrogen atom or an alkyl group having 1-18 carbon atoms, R19 is an alkylene group having 2-4 carbon atoms and f is an integer of 5-70, and
a polyoxyalkylene glycol glycerol ether represented by the general formula (5) 
wherein R20-R22 are each a hydrogen atom or an alkyl group having 1-18 carbon atoms, R23-R25 are each an alkylene group having 2-4 carbon atoms and g-i are each an integer of 5-7.
These conventional oils represented by the formulae (4) and (5) may be used singly or jointly for adding to the refrigerator oil of this invention. Further, the refrigerator oil of this invention may be incorporated with paraffinic mineral oils, naphthenic mineral oils, polyxcex1-olefins, alkylbenzenes and the like, but, in this case, the resulting mixed oil will be lowered in compatibility with hydrogen-containing halogonocarbons.
The amount of these conventional base oils so incorporated is not particularly limited as far as the excellent performances of the refrigerator oil of this invention are not impaired, but the esters [I]-[IV] should be present in the resulting mixed oil in a ratio of usually more than 50% by weight, preferably not less than 70% by weight of the total amount of the mixed oil.
To further improve the refrigerator oil of the present invention in thermal stability and chemical stability, it is incorporated with at least an epoxy compound. The epoxy compound used herein is preferably selected from the group consisting of phenylglycidyl ether epoxy compounds, alkylglycidyl ether epoxy compounds, glycidyl ester type epoxy compounds, aryloxyrane compounds, alkyloxirane compounds, alicyclic epoxy compounds, epoxidized fatty acid monoesters and epoxidized vegetable oils.
The said phenylglycidyl ether epoxy compounds used herein include phenylglycidyl ether and alkylphenylglycidyl ethers. The said alkylphenylglycidyl ethers are those having 1 to 3 alkyl groups having 1 to 13 carbon atoms, among which are preferred those having an alkyl group having 4 to 10 carbon atoms, such as n-butylphenylglycidyl ether, i-butylphenylglycidyl ether, sec-butylphenylglycidyl ether, tert-butylphenylglycidyl ether, pentylphenylglycidyl ether, hexylphenylglycidyl ether. heptylphenylglycidyl ether, octylphenylglycidyl ether, nonylphenylglycidyl ether and decylphenylglycidyl ether.
The alkylglycidyl ether epoxy compounds include decylglycidyl ether, undecylglycidyl ether, dodecylglycidyl ether, tridecylglycidyl ether, tetradecylglycidyl ether, 2-ethylhexylglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether. sorbitol polyglycidyl ether, polyalkylene glycol monoglycidyl ethers and polyalkylene glycol diglycidyl ethers.
The glycidyl ester type epoxy compounds include phenylglycidyl esters, alkylglycidyl esters and alkenylglycidyl esters with glycidyl 2,2-dimethyl octanoate. glycidyl benzoate, glycidyl acrylate, glycidyl methacrylate and the like being preferred.
The aryloxyrane compounds include 1,2-epoxystyrene and alkyl-1,2-epoxystyrene.
The alkyloxirane compounds include 1,2-epoxybutane, 1,2-epoxypentane, 1,2-epoxyhexane, 1,2-epoxyheptane, 1,2-epoxyoctane, 1,2-epoxynonane, 1,2-epoxydecane, 1,2-epoxyundecane, 1,2-epoxydodecane, 1,2-epoxytridecane, 1,2-epoxytetradecane, 1,2-epoxypentadecane, 1,2-epoxyhexadecane, 1,2-epoxyheptadecane, 1,1,2-epoxyoctadecane, 2-epoxynonadecane and 1,2-epoxyeicosane.
The alicyclic epoxy compounds include 1,2-epoxycyclohexane, 1,2-epoxycyclopentane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, exo-2,3-epoxynorbornane, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 2-(7-oxabicyclo[4.1.0]hept-3-yl)-spiro(1,3-dioxane-5,3xe2x80x2-[7]oxabicyclo[4.1.0]heptane, 4-(1xe2x80x2-methylepoxyethyl)-1,2-epoxy-2-methylcyclohexane and 4-epoxyethyl-1,2-epoxycyclohexane.
The epoxidized fatty acid monoesters include esters of an epoxidized fatty acid having 12 to 20 carbon atoms and an alcohol having 1 to 8 carbon atoms, phenol or an alkylphenol. In particular, butyl, hexyl, benzyl. cyclohexyl, methoxyethyl, octyl, phenyl or butylphenyl esters of epoxidized stearic acid may preferably be used.
The epoxidized vegetable oils include epoxidized compounds of vegetable oils such as soybean oil, linseed oil and cottonseed oil.
Among these epoxy compounds, the preferable ones include phenylglycidyl ether epoxy compounds, alkylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds and alicyclic epoxy compounds.
It is desirable that these epoxy compounds be incorporated in the refrigerator oil of the present invention in a ratio of 0.1-5.0% by weight, preferably 0.2-2.0% by weight, of the total amount of the refrigerator oil.
The refrigerator oil composition according to this invention may be incorporated further with at least one kind of a phosphorus compound selected from the group consisting of phosphoric esters, acid phosphoric esters, amine salts of acid phosphoric esters, chlorinated phosphoric esters and phosphorous esters, to improve the oil composition in wear resistance and load resistance. These phosphorus compounds are esters of phosphoric acid or phosphorous acid and an alkanol or a polyether type alcohol, or derivatives of the esters. The phosphoric esters are exemplified by tributyl phosphate, triphenyl phosphate and tricresyl phosphate. The acid phosphoric esters are exemplified by ditetradecyl acid phosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate, diheptadecyl acid phosphate and dioctadecyl acid phosphate. The amine salts of acid phosphoric esters are exemplified by salts of the above acid phosphoric esters and amines such as methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine and trioctylamine. The chlorinated phosphoric esters are exemplified by tris-dichloropropyl phosphate, tris chloroethyl phosphate, polyoxyalkylene bis[di(chloroalkyl)] phosphate and tris chlorophenyl phosphate. The phosphorous esters are exemplified by dibutyl phosphite, tributyl phosphite, dipentyl phosphite, tripentyl phosphite, dihexyl phosphite, trihexyl phosphite, diheptyl phosphite, triheptyl phosphite, dioctyl phosphite, trioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, triundecyl phosphite, didodecyl phosphite, tridodecyl phosphite, diphenyl phosphite, triphenyl phosphite, dicresyl phosphite, tricresyl phosphite and mixtures thereof. These phosphorus compounds may be added to the refrigerator oil in a ratio of 0.1-5.0% by weight, preferably 0.2-2.0% by weight, of the total amount of the refrigerator oil.
Of course, both of the aforementioned phosphorus compounds and epoxy compounds may be used jointly.
To further enhance the refrigerator oil of this invention in performances, the refrigerator oil may be incorporated, as required, with heretofore known additives for a refrigerator oil, which include phenol antioxidants such as di-tert.-butyl-p-cresol and bisphenol A; amine antioxidants such as phenyl-xcex1-naphthylamine and N,N-di(2-naphthyl)-p-phenylenediamine; wear resistant additives such as zinc dithiophosphate; extreme pressure agents such as chlorinated paraffin and sulfur compounds; oiliness improvers such as fatty acids; antifoaming agents such as silicone-type ones; and metal inactivators such as benzotriazole. These additives may be used singly or jointly. The total amount of these additives added is ordinarily not more than 10% by weight, preferably not more than 5% by weight, of the total amount of the refrigerator oil. The various additives which may be incorporated in the base oil and the epoxy compound according to this invention are collectively referred to as xe2x80x9can additive groupxe2x80x9d for brevity.
The refrigerator oils of this invention comprising at least one of the esters [I]-[IV] as the base oil should have such viscosity and pour point as those which are normally suitable for an ordinary refrigerator oil, but they should desirably have a pour point of not higher than xe2x88x9210xc2x0 C., preferably xe2x88x9220xc2x0 C. to xe2x88x9280xc2x0 C., to prevent them from solidification at a low temperature. Further, they should desirably have a kinematic viscosity of not less than 2 cSt, preferably not less than 3 cSt at 100xc2x0 C., to keep the sealability of the compressor when used, while they should desirably have a kinematic viscosity of not more than 150 cSt, preferably not more than 100 cSt at 100xc2x0 C., in view of their fluidity at a low temperature and the efficiency of heat exchange in the evaporator when used.
The refrigerants which may be used in refrigerators in which the lubricating oils (refrigerator oils) of the present invention are suitably used, include hydrogen-containing halogenocarbons such as alkane fluorides having 1-3 carbon atoms, preferably 1-2 carbon atoms and/or alkane chloride fluoride having 1-3 carbon atoms, preferably 1-2 carbon atoms. The said hydrogen-containing halogenocarbons are exemplified by HFCs (chlorine-free type halogenocarbons) such as difluoromethane (HFC-32), trifluoromethane (HFC-23), pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1-trifluoroethane (HFC-143a) and 1,1-difluoroethane (HFC-152a); HCFCs (chlorine-containing type halogenocarbons) such as monochlorodifluoromethane (HCFC-22), 1-chloro-1,1-difluoroethane (HCFC-142b), dichlorotrifluoroethane (HCFC-123) and monochlorotetrafluoroethane (HCFC-124); and mixtures thereof. Among these hydrogen-containing halogenocarbons, the chlorine-free type halogenocarbons such as HFC-32, HFC-23, HFC-125, HFC-134, HFC-134a and HFC-152a, are preferable in view of the environmental problems. The refrigerant used may suitably be selected from these halogenocarbons mentioned above depending on the purpose for which the resulting refrigerant is used as well as the properties which are desirable for the resulting refrigerant. The preferable refrigerants are exemplified by HFC-134a; a mixture of HFC-134a (60-80 wt %) and HFC-32 (40-20 wt %); a mixture of HFC-32 (50-70 wt %) and HFC-125 (50-30 wt %); a mixture of HFC-134a (60 wt %), HFC-32 (30 wt %) and HFC-125 (10 wt %); a mixture of HFC-134a (52 wt %), HFC-32 (23 wt %) and HFC-125 (25 wt %); and a mixture of HFC-143a (52 wt %), HFC-125 (44 wt %) and HFC-134a (4 wt %).
When the refrigerator oil of the present invention is used in a refrigerator, it is usually present in the form of a fluid composition for the refrigerator, which is a mixture of the refrigerator oil and a chlorine-free type halogenocarbon such as an alkane fluoride and/or an alkane chloride fluoride as mentioned above.
The present invention also relates to a fluid composition for a refrigerator, which comprises a chlorine-free type halogenocarbon refrigerant and a refrigerator oil according to the present invention.
The mixing ratio of the refrigerator oil and the refrigerant in the resulting composition is not particularly limited, but the refrigerator oil is usually comprised in an amount of 1-500 parts by weight, preferably in an amount of 2-400 parts by weight, based on 100 parts by weight of the refrigerant.
The refrigerator oils of the present invention are very excellent in compatibility with the hydrogen-containing halogenocarbons as compared with the heretofore known refrigerator oils. Further, the refrigerator oils of the present invention are excellent because they have not only high compatibility with the hydrogen-containing halogenocarbons and high electrical insulating property but also high lubricity, low hygroscopicity and high thermal and chemical stability.
The refrigerator oils of the present invention may particularly preferably be used in refrigerators, air-conditioners, dehumidifiers, cold-storage chests, freezers, freeze and refrigeration warehouses, automatic vending machines, showcases, cooling units in chemical plants, and the like which have a reciprocating or rotary compressor. Further, the above refrigerator oils may also preferably be used in refrigerators having a centrifugal compressor.
This invention will be better understood by the following Examples and Comparative Examples.